The invention concerns a grinding machine containing a machine frame having a work piece support surface and at least one grinding bar moveably mounted on the machine frame and extending transversely across the work piece support surface which grinding bar carries a grinding medium on its surface facing the work piece support surface and which grinding bar can be driven by means of an eccentric drive in a circular movement parallel to the work piece support surface in such a way that it travels in circles parallel to itself, the eccentric drive having at least two eccentric shafts which are directed perpendicularly to the work piece support surface and which are distanced from each other in the longitudinal direction of the grinding bar.
A grinding machine of this kind is known for example from EP 543 947 B1. In the solution described therein, the grinding bar is arranged on a beam via the eccentric drive, which beam is in its turn mounted on the machine frame via a second eccentric drive. The two eccentric drives run at different speeds so that the grinding bar carries out two overlapping circular movements of different diameters and different rotary speeds. Hereby overlapping and preferably non-linear grinding marks are to be produced so as to avoid the occurrence of significantly prominent grinding marks in the grinding pattern. The overlapping eccentric drives entail a considerable complexity of the construction. Moreover there is a problem in that great overhung masses are put into a fast circular motion eccentrically and the resulting imbalance cannot be completely balanced out even with the use of counter weights. Thus the grinding machine is caused to vibrate strongly during operation.
There are also numerous solutions in which several grinding units are arranged in series so that the grinding marks produced by the grinding units overlap each other. These solutions also require very complex constructions.